I. Field of the Invention
The present invention relates to devices for supporting flat ceramic objects to be fired in a continuously heating furnace.
II. Description of the Prior Art
It is known that ceramic objects, for example glazed wall or floor tiles, are fired in continuously heating furnaces. During this process the ceramic objects are placed upon rollers in the form of tubes which are rotated in the same direction, and the objects to be fired are moved through the furnace while positioned on the respective rollers. This means that the rollers simultaneously serve as a means of transport. The roller-type continuously heating furnaces are equipped with various zones having different temperatures corresponding to the temperature at which the glaze evaporates. The resultant vapors are deposited in the firing zone just ahead of the high temperature zone in a temperature range between 1050.degree. C. and 1150.degree. C. and in particular are also deposited on the rollers. As a result, the glaze can accumulate upon the rollers in this zone of the furnace covering a length of 8 to 10 meters. In the case of glazes with high alkali or lead oxide content, this may result in a thick layer within a period of time from several weeks to several months. The deposited glaze has strong adhesive properties so that the undersides of the objects to be fired adhere to the rollers during transport, resulting in clay particles being pulled out of the undersides of the ceramic objects which further increases the build-up layer on the tubes. In other familiar continuously heating furnaces, base plates are installed on the rollers which are moved through the furnace on the rollers. The material to be fired is placed on the base plates. The glaze vapor is deposited upon the rollers and plates to a very low degree and no particles are torn from the objects to be fired when employing this arrangement; however, the use of the base plates results in a higher energy consumption in continuous heating furnaces of this type.
In order to avoid the problem of the material to be fired adhering to the rollers in the continuous heating furnace, the rollers were equipped with a fireproof kaolin-engobe layer upon which the glaze precipitates but from which the precipitated material can be easily removed by grinding or sanding after the rollers have been pulled from the furnace and have cooled. This, however, necessitates an additional process step when firing objects which requires a greater expenditure of time and which renders the process less economical.
It is to this problem that the present invention applies. It is based upon the requirement to create a device for supporting flat ceramic objects to be fired in a continuous heating furnace, guaranteeing flawless support and transport of the objects to be fired in spite of the glaze precipitation without the material to be fired baking on the rollers.